The forgings will be hard if they are allowed to cool in air. This hardness varies over a range of from 250 to 500 Brinell, depending on the original forging temperature. ANNEALING can be done by heating to temperatures ranging from 1,290 to 1,380 deg.F. and cooling in air or quenching in water or oil. After this treatment the forgings will have a hardness of about 200 Brinell and a tensile strength of 100,000 to 112,000 lb. per square inch. If softer forgings are desired they can be heated to a temperature of from 1,560 to 1,650 deg.F. and cooled very slowly. Although softer the forgings will not machine as smoothly as when annealed at the lower temperature. HARDENING.--The forgings can be hardened by cooling in still air or quenching in oil or water from a temperature between 1,650 and 1,750 deg.F. The physical properties do not vary greatly when the carbon is within the range of composition given, or when the steel is hardened and tempered in air, oil, or water. When used for valves the following specification of physical properties have been used: Yield point, pounds per square inch 70,000 Tensile strength, pounds per square inch 90,000 Elongation in 2 in., per cent 18 Reduction of area, per cent 50 The usual heat treatment is to quench in oil from 1,650 deg.F. and temper or draw at 1,100 to 1,200 deg.F. One valve manufacturer stated that valves of this steel are hardened by heating the previously annealed valves to 1,650 deg.F. and cooling in still air. This treatment gives a scleroscope hardness of about 50. In addition to use in valves this steel should prove very satisfactory for shafting for water-pumps and other automobile parts subject to objectionable corrosion. TABLE 2.--COMPARISON OF PHYSICAL PROPERTIES FOR HIGH-CHROMIUM STEELS OF DIFFERENT CARBON CONTENT -------------------------------------------------------------------------- | C 0.20 | C 0.27 | C 0.50 | Mn 0.45 | Mn 0.50 | | Cr 12.56 | Cr 12.24 | Cr 14.84 -----------------------------------------|----------|----------|---------- Quenched in oil from degrees Fahrenheit | 1,600 | 1,600 | 1,650 Tempered at degrees Fahrenheit | 1,160 | 1,080 | 1,100 Yield point, pounds per square inch | 78,300 | 75,000 | 91,616 Tensile strength, pounds per square inch | 104,600 | 104,250 | 123,648 Elongation in 2 in., per cent | 25.0 | 23.5 | 14.5 Reduction of area, per cent | 52.5 | 51.4 | 33.5 --------------------------------------------------------------------------